1. Field of the Invention
The present invention relates to mineral processing, and more particularly, to a method and apparatus for separating metal values, such as nickel and nickel compounds, from mineral ores, including lateritic ores.
2. Discussion
Nickel is an important element and is used in a variety of products. It is often combined with other metals to form stainless steels and alloy steels, nonferrous and high temperature alloys. It is also used in electroplating, catalysts, ceramics and magnets.
Though nickel can be found in many different types of mineral deposits, currently only sulfide and lateritic ores can be mined economically using existing technology. In sulfide ores, nickel, iron and copper comprise a physical mixture of distinct minerals. This allows producers to concentrate the nickel present in sulfide ores using mechanical techniques, such as flotation and magnetic separation. Lateritic ores have a significantly different structure than sulfide ores. As a result, nickel producers cannot use straightforward mechanical or physical separation techniques to concentrate the nickel in lateritic ores, but instead must use chemical separation techniques.
One of the most promising chemical methods for obtaining nickel values from lateritic ores is called high pressure acid leaching. In the method, crushed and sized lateritic ore is placed in a pressure vessel with sulfuric acid. The mixture is agitated at high temperature and high pressure (e.g., 280° C., 5.4 MPa) to leach out nickel and cobalt. The resulting liquid phase, which includes dissolved nickel and cobalt, undergoes further processing to separate nickel and cobalt.
Though a useful technology, high pressure acid leaching suffers certain disadvantages. As currently practiced, high pressure acid leaching is carried out in a batchwise manner. Since nickel comprises only about one percent of a typical lateritic ore, the pressure vessel must be charged with large amounts of ore—e.g., one hundred tons of ore—to meet daily production requirements. This results in a large capital outlay for equipment. As compared to mechanical techniques, operating costs are high because the entire mixture must be heated to relatively high temperatures to extract a significant fraction of nickel and cobalt from the solid phase. Finally, disposal of spent sulfuric acid raises environmental concerns.
The present invention overcomes, or at least mitigates, one or more of the problems described above.